Potassium ions and endothelium-derived hyperpolarizing factor in guinea-pig carotid and porcine coronary arteries

1 Experiments were designed to determine in two arteries (the guinea-pig ca rotid and the porcine coronary arteries) whether or not the endothelium-der ived hyperpolarizing factor (EDHF) can be identified as potassium ions, and to determine whether or not the inwardly rectifying potassium current and the Na+/K+ pump are involved in the hyperpolarization mediated by EDHF. 2 The membrane potential of vascular smooth muscle cells was recorded with intracellular microelectrodes in the presence of N-omega-L-nitro-arginine ( L-NA) and indomethacin. 3 In vascular smooth muscle cells of guinea-pig carotid and porcine coronar y arteries, acetylcholine and bradykinin induced endothelium-dependent hype rpolarizations (-18+/-1mV, n = 39 and - 19 +/- 1 mV, n = 7, respectively). The hyperpolarizations were not affected significantly by ouabain (1 mu M), barium chloride (up to 100 mu M) or the combination of ouabain plus barium . 4 In both arteries, increasing extracellular potassium concentration by 5 o r 10 mM induced either depolarization or in a very few cases small hyperpol arizations which never exceeded 2 mV. 5 In isolated smooth muscle cells of the guinea-pig carotid artery, patch-c lamp experiments shows that only 20% of the vascular smooth muscle cells ex pressed inwardly rectifying potassium channels. The current density recorde d was low (0.5+/-0.1 pA pF(-1), n = 8). 6 These results indicate that, in two different vascular preparations, bari um sensitive-inwardly rectifying potassium conductance and the ouabain sens itive-Na+/K+ pump are not involved in the EDHF-mediated hyperpolarization. Furthermore, potassium did not mimic the effect of EDHF pointing out that p otassium and EDHF are not the same entity in those arteries.